Background

Psittacosis, also known as parrot fever, is an infection caused by the obligatory intracellular bacterium Chlamydia psittaci. The term psittacosis is derived from the Greek word for parrot, psittakos, and was first used by Morange in 1892.

This bacterium can infect parrots, parakeets, canaries, and other avian species (eg, turkeys, pigeons, ducks). Another term for this infection is ornithosis, which describes the infection caused by nonpsittacine birds.

The largest epidemic occurred in 1930 and affected 750-800 individuals. This epidemic led to the isolation of C psittaci in several laboratories in Europe and the United States.

Psittacosis is an occupational disease of zoo and pet-shop employees, poultry farmers, and ranchers. Human-to-human transmission is rare, but possible. These cases may cause more severe disease than avian-acquired psittacosis.

Psittacosis is probably underdiagnosed because patients with milder cases may not seek medical attention or may not be reported.
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Pathophysiology

The primary route for infection is through the respiratory system. Infection develops after organisms from aerosolized dried avian excreta or respiratory secretions from sick birds are inhaled. C psittaci attaches to the respiratory epithelial cells. After the initial inoculation, the organism spreads via the blood stream to the reticuloendothelial system. Subsequently, secondary bacteremia causes lung infection.

Humans may acquire disease by handling sick birds. Mouth-to-beak resuscitation has also been implicated in transmission. Transient exposure to infected birds may cause symptomatic infection, even in visitors to pet shops.

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Epidemiology

Frequency

United States

Reports show up to 200 cases of psittacosis annually. From 1988-97, the US Centers for Disease Control and Prevention (CDC) received 766 reports of psittacosis, which is probably an underestimate of the actual number of cases because psittacosis is difficult to diagnose, is covered by macrolide antimicrobials (which may be used empirically for therapy of community-acquired pneumonia), and often goes reported.

From 1988-2003, 935 human cases of psittacosis were reported to the CDC.
[2] From 2005-2009, 66 human cases of psittacosis were reported (mean, 13; range, 8-21) to the CDC through the Nationally Notifiable Diseases Surveillance System.
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International

Psittacosis is found worldwide. The incidence seems to be increasing in developed countries, which is correlated to the import of exotic birds.

Mortality/Morbidity

The mortality rate of psittacosis prior to the advent of antimicrobial treatment was approximately 15-20%. The mortality rate is less than 1% with appropriate antibiotic therapy.

Race

Psittacosis has no observed racial predilection.

Sex

Psittacosis has no observed sexual predilection.

Age

Psittacosis occurs in all age groups, including children. The infection is more common among individuals in the middle decades of life.

Committee of the National Association of State Public Health Veterinarians. Compendium of measures to control Chlamydia psittaci infection among humans (psittacosis) and pet birds (avian chlamydiosis), 2000. Centers for Disease Control and Prevention. Morbidity Mortality Weekly Reports. 2000. 49:3-17. [Medline].